Delivery systems for administering a beneficial agent to a biological, fluid environment of use are known to the prior art. For example, U.S. Pat. No. 3,845,770 issued to Theeuwes and Higuchi, and in U.S. Pat. No. 3,916,899 issued to the same patentees, a device is disclosed comprising a wall that surrounds a compartment containing a beneficial agent. The wall is permeable to the passage of fluid and comprises a passageway that is preformed or formed during use through the wall for delivering the beneficial agent from the device. The devices of these patents release the beneficial agent by fluid being imbibed through the wall into the compartment at a rate determined by the permeability of the wall and the osmotic pressure gradient across the wall. The fluid imbibed into the device mixes with the beneficial agent to form an aqueous solution comprising the beneficial agent that is dispensed through the passageway from the device. The devices of these patents are extraordinarily effective for delivering a beneficial agent that is stable and soluble in aqueous and biological fluids and exhibits an osmotic pressure gradient across the wall against the fluid. The devices are effective also for delivering a beneficial agent that is mixed with an osmotically effective solute soluble in fluid that exhibits an osmotic pressure gradient across the wall against an aqueous fluid.
A further advancement in the delivery art for dispensing a stable formulation is disclosed in U.S. Pat. No. 3,995,632 issued to Nakano, Higuchi and Hussain. The dispenser disclosed in this patent dispenses a stable composition that absorbs heat and forms a dispensable melt. The melt is dispensed by a solution of magnesium sulfate increasing in volume and occupying the space originally occupied by the melt.
A quantum improvement in osmotic devices-was presented to the pharmaceutical dispensing art by inventor Theeuwes in U.S. Pat. Nos. 4,111,202; 4,111,203; and 4,203,439. In these patents the delivery kinetics of the devices were enhanced for delivering a beneficial agent with different degrees of solubility in an aqueous-type fluid. The kinetics were improved by manufacturing the devices with a beneficial agent compartment separated by a film from an osmotic compartment. The devices deliver the beneficial agent by fluid being imbibed through the wall into the osmotic compartment to fill the compartment with fluid that acts as a driving force and causes the film to move. The film moves against the beneficial agent compartment and the driving force pushes the beneficial agent through a passageway from the device.
A pioneer advancement in osmotic delivery devices was made by Cortese and Theeuwes in U.S. Pat. No. 4,327,725 and by Wong, Barclay, Deters and Theeuwes in U.S. Pat. No. 4,612,008. The devices disclosed in these patents comprise a semipermeable wall that surrounds a compartment. The compartment contains a beneficial agent formulation and a hydrogel. These devices operate by imbibing fluid into the compartment, wherein it contacts the biological agent formulation and forms a dispensable aqueous formulation, and wherein it contacts the hydrogel causing it to expand and push the dispensable aqueous formulation from the device.
The delivery devices described in the above patents operate successfully for their intended use and they can deliver many beneficial agents for their intended effects. Now, it has been observed their use can be limited because they lack the necessary elements to deliver beneficial agents that are sensitive to fluids, and to fluids containing biological gases. Their use may be limited because beneficial agents that are sensitive to such aqueous-biological fluids or to other fluids external to the delivery device may be adversely affected by fluids that enter the device and contact the beneficial agents during operation of the device. Examples of such fluid sensitive agents include proteins and peptides, and hormones. Moreover, the prior art devices lack the necessary means for their use as implant devices for dispensing such sensitive agents to a biological fluid-rich environment of use.
It will be appreciated by those versed in the dispensing arts that if a delivery system is provided for administering at a controlled rate and for protecting a beneficial agent that is sensitive to aqueous and biological fluids, and which delivery system possesses the kinetic ability to deliver the protected beneficial agent in effective amounts over time, such a delivery system would have a positive value and represent an advancement in the dispensing arts. Likewise, it will be self-evident to those versed in the implant art that a pressing need exists for an implant that is essentially-free of the tribulation associated with the prior art, and, that if such an implantable delivery system is provided, it would have a practical application in the fields of human and veterinary medicine and in the breeding and management of farm animals.